In general, an air conditioner for a vehicle is an apparatus for cooling or heating the interior of the vehicle by cooling or heating through the process of introducing outdoor air into the interior of the vehicle or circulating indoor air of the vehicle. Such an air conditioner for a vehicle includes an evaporator for cooling the inside of an air-conditioning case; a heater core for heating the inside of the air-conditioning case; and a mode converting door for selectively blowing the air cooled by the evaporator or heated by the heater core toward parts of the interior of the vehicle.
FIG. 1 illustrates an example of the air conditioner for a vehicle. As shown in FIG. 1, the air conditioner includes: an air-conditioning case 10 which has an air inflow port 11 formed at an inlet side thereof and a plurality of air outflow ports formed at an outlet side thereof; an evaporator 1 and a heater core 2 mounted inside the air-conditioning case 10; a temp door 20 mounted between the evaporator 1 and the heater core 2 to control temperature; and mode doors 30 which are respectively mounted at the air outflow ports 12 to adjust the degree of opening of the air outflow ports 12 according to air-conditioning modes.
Such an air conditioner carries out heating by circulating coolant, which is heated by an engine, in the heater core 2. However, at the early stage of starting the engine, because temperature of the coolant is low, the air conditioner cannot carry out heating using the coolant. Therefore, as an auxiliary heating device for heating at the early stage of starting the engine, a PTC heater 5 is used to heat using an electric energy of a battery.
Moreover, such a positive temperature coefficient (hereinafter, called ‘PTC’) heater 5 is installed on an air conditioner for recently developed electric vehicles. Because the heater core 2 using combustion heat of the engine cannot be mounted in the air conditioner for electric vehicles, the PTC heater 5 serves as a main heating device.
FIG. 2 illustrates a PTC heater. The PTC heater 5 is configured in such a way that a plurality of heating rods 6, in each of which a PTC element and a (+) terminal are embedded, and a plurality of heating rods 6, in each of which a PTC element and a (−) terminal are embedded, are arranged to be spaced apart from each other at a predetermined interval and radiation fins 7 are interposed between the heat rods 6.
A control unit 8 having a voltage control element (not shown) for controlling voltage supplied to the (+) terminal and the (−) terminal of the heating rods 6 is mounted at one side of the PTC heater 5.
Therefore, the PTC heater can variably control voltage supplied to the PTC heater 5 through a duty ratio control of a pulse width modulation (PWM) signal corresponding to a set temperature of the interior of the vehicle.
In other words, the voltage control element of the control unit 8 of the PTC heater 5 can vary voltage supplied to the terminal of each heating rod 6 by a duty ratio of the PWM signal, and in this instance, output temperature (heat value) of the PTC element attached to the terminal is varied, such that air passing through the radiation fins 7 is heated.
Moreover, as shown in FIG. 2, a single PTC heater 5 is mounted on the air-conditioning case 10 of a general air conditioner, but in the case that the inside of the air-conditioning case 10 like air conditioners, each of which has an independent control function at the right and the left (a driver's seat and a passenger's seat), is divided into a left passageway 10a and a right passageway 10b by a separator 13, as shown in FIG. 3, two PTC heaters 5 are respectively mounted at the left passageway 10a and the right passageway 10b inside the air-conditioning case 10 one by one to provide a perfect independent control at the right and the left.
However, if the two PTC heaters 5 are mounted on the air-conditioning case 10, it increases manufacturing costs and weight of the air conditioner, and deteriorates vehicle fuel efficiency and productivity.